DMAENGINE: add runtime slave config to DMA40 v3

This extends the DMA engine driver for the DMA40 used in the
U8500 platform with the generic runtime slave configuration
interface.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>